a) Field of the Invention
The present invention relates to a spindle motor, and more particularly to a spindle motor using a dynamic pressure type bearing.
b) Description of the Related Art
A brushless multi-phase d.c. motor has been used for driving a magnetic disc. This type of motor is called a spindle motor having a stator with a stator coil for generating a magnetic field, and a rotor with rotor magnets for receiving a rotation force in cooperation with the magnetic field.
As disc drives are becoming more and more compact, there is a strong need for a compact spindle motor. In order to comply with such a need, a technique has been studied to use a dynamic pressure type bearing between a stator and a rotor of a spindle motor. An example of the dynamic pressure type bearing structure is disclosed, for example, in Japanese Patent Laid-open No. 3-60355. In this structure, herringbone shaped grooves are formed on the radial contact surface between the rotor and stator. The rotation of the rotor pressurizes a lubricating fluid filled in the grooves so that a force is generated to provide a space between the rotor and stator. This force functions as a radial direction bearing.
For a dynamic pressure type thrust direction bearing, a spiral groove is formed on the end surface of a shaft of the rotor. A pumping operation generated by the rotation of the shaft pressurizes the lubricating fluid to raise the shaft.